We shall study the mechanism of homing of IgA precursor cells from gut-associated lymphoid tissue to secretory sites and attempt to demonstrate that such cells taken from orally immunized mice can transfer a specific IgA antibody response to the lactating mammary gland. We shall also study the influence and role of hormones in this phenomenon. Other aspects of our work are concerned with how secretory component is covalently linked to IgA and whether a disulfide interchange enzyme could play a role in this process.